The following information pertains to a semigravity retaining wall with clean sandy soil as backfill (following page): Total height of wall stem H = 6 m, width of wall stem (top) = 1 m, width of wall stem (bottom) = 2m, J = 18.2 kN/m3 (moist unit weight), I’ = 28o (from CD triaxial test), c’ = 0 (sandy soil), G = 14o (soil-wall friction angle???D = 10o (inclined backfill), and E = 85o (same for the inside and outside faces). (A) Determine the Coulomb maximum active force per unit length of wall using the
trial-wedge based graphical method. (B) Compare the maximum active force obtained in part (A) with that calculated from
Coulomb’s analytical solution and draw a brief conclusion.
NOTE 1: You are required to redraw the cross section of the combined wall-backfill geometries to exact scale (the larger the better).
NOTE 2: For each trial wedge in part (A), you are required to draw a separate force
polygon to exact scale. NOTE 3: You are required to plot the change in the active force magnitude with
increasing trial-wedge angle T using MS Excel software. NOTE 4: You are welcome to use advanced plotting software, such as AutoCAD, for
the combined wall-backfill geometries and/or the force polygons, but is not required.
EXERCISE 2 (50 PTS)
The following information pertains to a cantilever retaining wall that is being designed as part of a recreational, open-channeled, waterways project as shown (following page): x H? = 10 ft (thickness of sandy soil) x H? = 15 ft (thickness of clayey sandy soil) x H? = 10 ft (lowest water table expected on the outside face of the wall) x J? = 110 pcf (moist unit weight), I’? = 30
o , and c’? = 0 (sandy soil)
x J? = 136 pcf (saturated unit weight), I’? = 28
o , and c’? = 215 psf (clayey sandy soil)
In addition, a surcharge load (accounting for parking and restroom facilities next to the wall) is being considered: x q = 1000 psf, a’ = 10 ft, and b’ = 8 ft Determine the Rankine net active force per unit length of wall. NOTE 1: The net active force is to be calculated based upon the resulting (combined)
lateral pressure distribution diagrams. NOTE 2: Hydrostatic pressures acting on both the inside and the outside faces of the
wall must be taken into account in calculating the net active force. NOTE 3: Use at least 5 equally spaced depth intervals in assessing the lateral pressure
diagram from the 1000-psf surcharge.
NOTE 4: You are required to plot the resulting lateral pressure distribution diagrams from backfill soils, surcharge load, and inside and outside hydrostatic pressures, to exact scale.
NOTE 5: You are required to follow the same step-by-step approach documented in
your class notes for solving similar examples, including calculation tables. NOTE 6: You are welcome to use advanced plotting software, such as AutoCAD, for
the pressure diagrams, but is not required.
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